Tracer diffusion from a horizontal fracture into the surrounding matrix: Measurement by computed tomography

Amir Polak, Abraham S. Grader, Rony Wallach*, Ronit Nativ

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The vertical diffusion of NaI solution from a horizontal fracture into and within the surrounding matrix was tracked and quantified over time using an artificially fractured chalk core (30×5 cm) and a second-generation X-ray computed tomography (CT) scanner. The different tracer-penetration distances imaged in the matrix above and below the horizontal fracture are indicative of a greater tracer mass penetrating into the lower matrix. The enhanced transport in the matrix below the fracture was related to the Rayleigh-Darcy instability induced by the density differences between the heavier tracer solution in the fracture (1.038) and the distilled water that had initially resided in the matrix. Our observations suggest that below the fracture, the tracer is propagated by an advection-diffusion process that is characterized by both higher rates and higher concentrations relative to its propagation by diffusion above the fracture. The experimental results suggest that the prediction of contaminant migration in a rock intersected by both vertical and horizontal (e.g. along bedding planes) fractures is difficult because of density effects that result in different solute-penetration rates.

Original languageAmerican English
Pages (from-to)95-112
Number of pages18
JournalJournal of Contaminant Hydrology
Issue number1-4
StatePublished - Dec 2003

Bibliographical note

Funding Information:
Funding for this research was provided by The Ramat Hovav Industrial Council and the EU under contract no. ENV-CT97-0441. The Baron De Hirsch Fund provided travel money from Israel to Penn State University. We wish to thank Abdullah Al-Ajmi and Ozgen Karacan at Penn State University for their help with the CT experiments. We are grateful to Luis Moreno and a second anonymous reviewer for their useful remarks.


  • CT imaging
  • Chalk
  • Density-induced instability
  • Diffusion
  • Fractured rock


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